1. Field of the Invention
The present invention relates to a modular endless belt conveyor device provided with means for guiding said belt in the curved path portions.
2. Description of the Related Art
This type of belt, generally made of thermoplastic, as described in document U.S. Pat. No. 5,573,105, may comprise intrinsic means which allows its guidance to be improved, in particular at the curved portions of the conveyor. In fact, the key concern is to reduce the friction between the belt and its supporting structure and, as far as possible, to overcome the consequences of such friction which can vary to significant degrees depending on the magnitude of the load carried along by the upper strand of said belt.
The consequences of such friction are many. First of all, there is the heating between the moving parts, that is to say the belt and the fixed parts formed by the various elements of the supporting structure of said belt; there is also the wear on the belt, which is made of thermoplastic, and another significant consequence is the instability of said belt. Specifically, under the effect of the load and the tension, the belt may tend to rise at its outer periphery when negotiating the curves.
There are solutions for reducing the friction between the belt and the structure of the conveyor. As described in the aforementioned document, the belt may include rollers which are mounted so as to project from its inner surface, and these rollers are arranged over the whole length of the belt, being fastened by suitable means, so as to cooperate with a curved guide situated at each curved part of said conveyor.
In addition to their specific function associated with the curvilinear guidance of the belt, the rollers can also stabilize the belt against the risks of the upper strand rising in the curved portions of the conveyor.
To perform this belt-stabilizing function, the rollers disclosed in the aforementioned document cooperate with an arrangement of the fixed curved guide, which arrangement takes the form of a continuous rim which is arranged so as to project with respect to the active running surface of said guide, which rim extends between said rollers and the inner surface of the belt.
In another embodiment, this function of stabilizing the upper strand of the belt in the curved parts of the conveyor is provided by means of a curved guide which is arranged at the outer periphery of said curved parts, and this guide cooperates with protuberances in the form of an angle bracket, or hook, which are arranged so as to project from the inner surface of the peripheral rim of said belt.
There also exists, as described in document U.S. Pat. No. 3,094,206, other types of conveyor belts, non-modular ones, which have rollers cooperating with a guide in the curved parts. In that document, rollers are also arranged directly on the curved frame in order to reduce friction and improve guidance.
In document U.S. Pat. No. 6,129,202, the conveyor belt does not have rollers but protuberances arranged so as to project from its inner surface, and these protuberances cooperate with rollers which are arranged only on what acts as a frame in the curved part of the conveyor. These rollers make it possible to reduce the friction and they additionally have a groove which cooperates with a kind of lug arranged at the lower part of each protuberance so as to stabilize the belt and keep it flat.